There are too many variable to discuss and go into when we ask this question, so I'll use an analogy instead.
You don't go to work because you enjoy it, right? You go to work because you have bills to pay, and yes, you probably complain about it and you probably don't go to work with lots of enthusiasm, but you go to work regardless.
Depending on your type of work, you go to work 3-5 days of the week.
Well, with training, it's the same thing. You don't go training to have fun, you go training to earn your goals, like you to go to work to earn your money.
So, with this in mind, it really doesn't matter if you train 1, 2 or 3x a week, what matters is the work you put in when you DO train.
If you just do the same thing over and over and over, you aren't physiologically stressing the muscle, and thus you aren't allowing the muscle to adapt to a stimulus, and it won't grow and you won't tone up, no matter how many days a week you train.
IF you train just once a week, focusing on your back and arms, because this is the body part you really care about changing, but you push yourself, and you increase the weight, or the reps, or both, or increase time under tension, you will EARN a better physique.